[PATCH] drm/amdgpu: fix fence slab teardown

[Grazvydas Ignotas]

To free fences, call_rcu() is used, which calls amdgpu_fence_free()
after a grace period. During teardown, there is no guarantee all
callbacks have finished, so amdgpu_fence_slab may be destroyed before
all fences have been freed. If we are lucky, this results in some slab
warnings, if not, we get a crash in one of rcu threads because callback
is called after amdgpu has already been unloaded.

Fix it with a rcu_barrier().

Fixes: b44135351a3a ("drm/amdgpu: RCU protected amdgpu_fence_release")
Signed-off-by: Grazvydas Ignotas <notasas at gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
index 3a2e42f..77b34ec 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_fence.c
@@ -68,6 +68,7 @@ int amdgpu_fence_slab_init(void)
 
 void amdgpu_fence_slab_fini(void)
 {
+	rcu_barrier();
 	kmem_cache_destroy(amdgpu_fence_slab);
 }
 /*
-- 
2.7.4